Method and arrangement for determining the size and/or the shape of a freely falling object

ABSTRACT

Disclosed is a method and an arrangement for determining the shape and/or size of a freely falling drop (1) of molten glass. One end of the drop is detected by means of two photo-diodes (7,8) spaced apart along the fall path for determining the fall speed of the drop. An image of that part of the drop located momentarily between the two photo-diodes (7,8) is projected onto an elongated photo-diode array (9) extending perpendicularly to the fall direction. The photo-diode array (9) is scanned periodically at a given time interval a large number of times during movement of the drop past the array. This provides information relating to the width of the drop at a large number of locations along the length of the drop. The mutual distance between these width determinations are calculated on the basis of the fall speed of the drop and the time interval between the different scans. The shape and size of the drop is calculated from these data.

The present invention relates to a method and to a correspondingarrangement for determining size and/or shape of a freely falling objectparticularly a drop of liquid or semi-liquid material, such as moltenglass in particular. The invention has been developed primarily for thepurpose of determining the size and shape of freely falling drops ofmolten glass, but can also be applied for determining the size and shapeof other objects.

In the automated manufacture of container glass and like products, theproduct is formed from a so-called glob which is fed to the mouldthrough a chute. The glass glob has a temperature of 1000°-1100° C. andis ejected through a nozzle in the bottom of a molten-glass feederchannel or tank and is clipped off or sheared in suitable lengths,contingent on the product being produced, e.g. a length of 75-150 mm.One and the same chute may supply several different moulds with glassdrops or globs in sequence, so that a glass drop is supplied to an emptymould while earlier filled moulds are being worked. Thus, it is normalfor 2-3 glass drops/second to be ejected from the nozzle and clipped-offadjacent thereto. With this type of manufacture of glass products, theshape, volume and temperature of the glass drops have a greatsignificance on the quality of the end product. Although the parameterscan be influenced in several ways, there are at present no devices orapparatus by means of which these parameters can be measured,particularly the shape and volume of the glass drops. Consequently, thistype of automated manufacture of glass products has been controlled to alarge extent by "instinct", which makes it difficult to maintain auniform quality of the products produced and to reproduce a productionapproach that has been found to give good results.

The object of the invention is therefore to provide a method and acorresponding arrangement by means of which the shape and/or size of afreely falling object can be determined, and particularly, but notexclusively the volume and shape of a freely falling drop of moltenglass.

The characterizing features of the inventive method and arrangement areset forth in the following respective claims.

The invention will now be described in more detail with reference to theaccompanying drawings, in which

FIG. 1 illustrates schematically an arrangement according to theinvention;

FIG. 2 is a schematic illustration of the FIG. 1 arrangement seen atright angles to the view in FIG. 1; and

FIG. 3 illustrates schematically the inventive method for determiningthe volume and shape of the falling object.

The drawings illustrate the application of the invention for determiningthe shape and volume of a freely falling drop of molten glass.

FIG. 1 illustrates schematically a drop of glass 1 which falls in thedirection shown by the arrow 2, the glass drop, or corresponding glassmass, being shown in full lines and in broken lines corresponding to twodifferent positions of the drop 1 during its fall. The inventivearrangement comprises a suitable optical device or system 3, which isonly illustrated schematically and which images on an imaging plane 4that part of the glass drop 1 which is located momentarily opposite theoptical instrument 3. The optical device, in this regard, is designed toimage in the plane 4 slightly more than that part of the glass drop 1which is located momentarily between two levels 5 and 6 which are spacedapart through a given distance s in the fall direction 2 of the glassdrop 1. The illustrated arrangement also includes two photo-diodes 7 and8 which are positioned behind respective elongated narrow measuringslots 7a and 8a (c.f. FIG. 2) located in the image plane 4 at a mutualspacing corresponding to the distance s between the two levels 5 and 6.Arranged centrally between the two photo-diodes 7 and 8 is an elongatedarray 9 which includes a large number of mutually adjacent photo-diodesarranged behind an associated, elongated narrow measuring slot 9alocated in the image plane 4 (c.f. FIG. 2). Similar to the diode array9, this measuring slot 9a has a length extension which will ensurepositively that the full width of the image of the glass drop 1projected in the image plane 4 will fall within the measuring slot 9aand the diode array 9. The two photo-diodes 7, 8 and the diode array 9are connected to a control-and-arithmetical unit 10, the constructionand method of operation of which will be described hereinafter.

When the lower end of the falling drop of glass 1 reaches the level 5,the character of the output signal from the photo-diode 7 changes, whilein the same way the character of the output signal on the photo-diode 8changes when the lower end of the glass drop 1 reaches the level 6 alittle later on. The output signals from the photo-diodes 7 and 8 areapplied to the control-and-arithmetical unit 10, which is constructed tocalculate the time difference between the said changes in the outputsignals from the photo-diodes 7 and 8 and to calculate on the basis ofthis time difference and the known distance s between the levels 5 and6, the average speed of the glass drop 1 during the time taken for thelower end of the glass drop 1 to move from the level 5 to the level 6,in accordance with the formula

    V.sub.1 =s/t.sub.1

where t₁ is the time for the lower end of the glass drop 1 to pass fromlevel 5 to level 6, determined by means of the diodes, and V₁ is theaforesaid average speed, hereinafter referred to as the drop entryspeed. This speed differs negligibly from the speed of the drop 1 atthat moment when the lower end of the drop passes the level between thelevels 5 and 6, i.e. the level on which the diode array 9 is located.

The control-and-arithmetical unit 10 is constructed to scan the diodearray 9 periodically, at a given time interval, during the whole of thetime taken for the falling glass drop 1 to pass the level of the diodearray 9. This scanning process can be initiated automatically, e.g. whenthe lower end of the glass drop 1 reaches the level 5 and the characterof the output signal of the photodiode 7 changes therewith, and can beinterrupted automatically when the upper end of the glass drop 1 reachesthe level 6 and the character of the output signal from the photo-diode8 is again changed. Each scanning of the diode array 9 should take placeso rapidly that the fall distance of the drop 1 is no greater than 0.3mm during the scanning process. Scanning of the diode array 9 can beeffected rapidly even when the array contains a large number of diodes,e.g. by dividing the array into a multiple of sections which are scannedin parallel. The time interval between mutually sequential scans shouldbe so short that the distance through which the glass drop falls betweentwo mutually sequential scans of the array 9 will not exceed ca 1-2 mm.The resolution and measuring accuracy of the system become greater withgreater numbers of diodes in the array, with faster scanning of thediode array, and with shorter time intervals between mutually adjacentscans.

During a scanning of the diode array 9, the character, i.e. the signallevel, of the output signals from the diodes located within the image ofthe glass drop 1 projected in the image plane 4 is different to thecharacter of the output signals emanating from those diodes which lieoutside the image.

The control-and-arithmetical unit 10 may, advantageously, be constructedto accept solely output signals from those diodes in the array 9 whichlie within the image of the drop 1. It will be perceived that the numberof such diodes will constitute a direct measurement of the width of thedrop 1 in the projection of the image plane 4. If it is assumed that thedrop has a circular cross-section, this width measurement will also bethe diameter of the drop. The output signals received from thephoto-diodes of the array 9, and therewith information relating to thewidth or diameter of the drop at the scanning location, areadvantageously stored in a memory, suitably a RAM-memory, in thecontrol-and-arithmetical unit 10.

Thus, during periodic scanning of the diode array 9, as the glass drop 1moves past the array, there is obtained a series of width or diametervalues for mutually different locations along the extent of the glassdrop, as illustrated schematically in FIG. 3, where the numbered orderof sequence is designated n=1, 2, 3, etc. and the corresponding width ordiameter values are designated d₁, d₂, d₃, etc.

An advantage is also afforded when, with each scanning of the diodearray 9, it is established which diode in the array is the first diode,seen from one end of the array, which lies within the projected image ofthe glass drop 1. This provides information relating to the position ofthe image, and therewith the drop 1, in the lateral direction, thisinformation being designated r₁, r₂, r₃, etc. in FIG. 3 and also beingstored in the RAM-memory in the control-and-arithmetical unit 10.

Since all of the aforesaid measurement values obtained from a glass drop1 are stored intermediately direct into a RAM-memory in thecontrol-and-arithmetical unit 10, a very high scanning speed and datatransfer speed to the RAM-memory in the unit 10 can be achieved withoutlimitations caused by the hardware and/or software in the unit 10. Whenall the measurements of a glass drop 1 have been taken, the informationstored in the RAM-memory can be processed by the unit 10.

As beforementioned, this information consists of:

the time t₁ taken for the lower end of the glass drop 1 to pass betweenthe levels 5 and 6, i.e. through the distance s;

the number n of scans of the diode array which have provided anyinformation;

the width or diameter d_(n) of the drop at each scan made by the array9;

the lateral position r_(n) of the drop 1 at each scan of the array 9.

The unit 10 is constructed to calculate the distance, seen in the falldirection or length direction of the drop 1, between the different widthor diameter measurements, on the basis of the aforesaid information.This distance is referenced h₁, h₂, h₃, etc in FIG. 3. It will beunderstood that these distances correspond to the distance through whichthe glass drop 1 falls between the different scans of the diode array.The unit 10 calculates these fall distances with the aid of the formula

    h.sub.n =v.sub.1 t+(n-1)at.sup.2 +at.sup.2 /2

where n is the numerical order of the actual array scan concerned, t isthe time interval between mutually sequential scans, a is thegravitational acceleration 9.81 m/s², and v₁ is the entrance speed ofthe glass drop 1 calculated in the aforedescribed manner by means of theformula

    v.sub.1 =s/t.sub.1

The arithmetical unit 10 is able to calculate the total volume of theglass drop 1 with the aid of this data, by calculating for each diametervalue the volume of a cylinder which has the particular diameter d_(n)and the height h_(n) to the next diameter value, i.e.

    vol.sub.n =πd.sub.n.sup.2 h.sub.n /4

whereafter the total volume of the glass drop 1 can be obtained byadding up all part volumes vol_(n), i.e. ##EQU1## Furthermore, the totallength or height h_(tot) can be obtained by adding up all part heightsh_(n), i.e. ##EQU2## Connected to the control-and-arithmetical unit 10is a display unit 11 which has the form of a display screen and/or aprinter by means of which desired information relating to the glass dropcan be presented visually and/or printed out. In this regard, it is alsopossible to show or to draw the shape of the glass drop, i.e. in theform illustrated in FIG. 3.

It has been assumed in the aforegoing that the glass drop has anessentially circular cross-sectional shape. If this assumption does notapply with any degree of certainty, a further diode array with anassociated optical device can be arranged for scanning the glass drop orglob in a direction perpendicular to the scanning direction of the firstdiode array. In this case there are obtained two mutually perpendicularwidth values of the glass drop with each scan effected simultaneously bythe diode arrays, thereby enabling the volume of the drop to becalculated to an acceptable degree of accuracy despite the fact that thedrop does not have a completely circular cross-sectional shape.

When measuring a falling drop or glob of the molten glass which has atemperature of ca 1000°-1100° C., both the photodiodes 7, 8 and thephoto-diodes array 9 can work with the radiation emitted by the actualglass drop itself and hence no additional illumination need be used.

Although the invention has been developed primarily for determining thesize and shape of the falling drop of molten glass, as before described,it will be understood that the invention can be used generally fordetermining the size, shape or position of any freely falling bodywhatsoever. In these latter applications it may be necessary toilluminate the object. This can be achieved by either illuminating thefront side or the rear side of the object, as seen in relation to thelocation of the optical system.

I claim:
 1. A method of determining the shape and/or the size of afreely, falling object, particularly of a drop of liquid or semi-liquidmaterial, such as molten glass in particular, characterized byopticallydetecting one end of the object (1) at two positions (5, 6) located at agiven distance apart in the fall path (2) of the object, and determiningthe time difference between said two detections; calculating the speedat which the object falls during movement of said detected end betweenthe two detection locations from said time difference and the distance(s) between the detection locations; projecting, during the fall of theobject past the detection locations, that part of the object which islocated between the detection locations at each moment in time onto anelongated array (9) of a large number of mutually adjacent radiationdetectors extending transversely to the fall direction of the object;scanning said array (9) periodically at a given time interval a largenumber of times during the fall of the object past the array; preservinginformation obtained from each scanning of the array relating to thenumber of detectors in the array which during the scan were covered bythe image of the object projected onto the array, and therewithinformation concerning the width of the object; calculating from saidcalculated speed and said given time interval the values of the distancethrough which the object falls between the different scans of the array(9); and using the said width values and said fall distances fordetermining the size of the object.
 2. A method according to claim 1,characterized by preserving from each scan of the array (9) informationindicative of which radiation detector in the array is located at oneedge of the object image projected on the array and therewithinformation indicative of the position of the object in a lateraldirection at the moment of the scan in question, and constructing thecontours of the object in the projection plane with the aid of saidinformation relating to the width of the object and the lateral positionthereof at the moment of each scan, together with said calculated falldistance of the object between the different scans.
 3. A methodaccording to claim 1, in which the object consists of a drop of liquidor semi-liquid material, particularly molten glass, characterized inthat the volume of the drop (1) is determined by calculating for each ofsaid width values the volume of a cylinder whose diameter is said widthvalue and whose height is the calculated fall distance between the arrayscan corresponding to the width value concerned and the nearest scan intime, and by adding together the thus calculated volumes for all widthvalues.
 4. A method according to claim 1, characterized by projecting afurther image of the object, at right angles to the projection directionof the first mentioned image, onto a further elongated array of mutuallyadjacent radiation detectors, said further array being arranged on thesame level as the first mentioned array but at right angles thereto, andby scanning said further array in the same manner as the first mentionedarray and processing the thus obtained information in a correspondingmanner to the information obtained when scanning the first mentionedarray.
 5. An arrangement for determining the shape and/or size of afreely falling object (1), particularly a drop of liquid or semi-liquidmaterial, such as molten glass in particular, characterized in that itincludestwo radiation detectors (7, 8) which are located at a mutualdistance (s) apart along the path through which the object falls andwhich are operative in detecting the falling object and to produce acharacteristic output signal when one end of the object passes thedetector in question; an elongated array (9) of a large number ofmutually adjacent radiation detectors which is arranged between the twofirst mentioned radiation detectors (7, 8) perpendicularly to the falldirection (2) of the object (1); an optical device (3) for projectingonto the array (9) an image of that part of the object which is locatedopposite the array (9) at any moment in time; and acontrol-and-arithmetical unit (10) which is arranged: to receive saidoutput signals from the two first mentioned radiation detectors (7, 8)and, on the basis of the time difference between the signals and thegiven distance (s) between the two first mentioned radiation detectors(7, 8), to calculate the fall speed of the object (1) when the detectorend of the object passes said detectors; to scan said array (9)periodically at a given time interval, and to receive from the array (9)output signals indicative of which of the radiation detectors in saidarray (9) were located within the object image projected on the arrayduring a scan; to establish with each scan of the array (9) the numberof radiation detectors which lay within the projected object image, andtherewith establish the width of the image and the object; to calculatethe distances through which the object falls between the various scanson the basis of the established fall speed and said given time intervalbetween the scans of the array (9); and to determine the size and/or theshape of drop on the basis of the width values of the object at thedifferent scans and said values of the distance through which the objectfalls between the different scans.
 6. An arrangement according to claim5, characterized in that the control-and-arithmetical unit (10) is alsoconstructed to establish with each scan of the array (9) which of thedetectors in said array is the first detector, seen from one end of thearray, which lies within the projected image of the object (1) andtherewith establish the lateral position of the image and the objectduring the scan in question.
 7. An arrangement according to claim 5characterized in that the control-and-arithmetical unit (10) includes aRAM-memory which is constructed to receive and to store intermediatelythe output signals from the two first mentioned detectors (7 and 8) andthe array (9) for subsequent processing of the signals.
 8. Anarrangement according to claim 5, characterized in that it furtherincludes a display unit (11) which is connected to thecontrol-and-arithmetical unit (10) and which has the form of a displayscreen and/or a printer for presenting and/or printing measured andcalculated data relating to the size and/or the shape of the object. 9.An arrangement according to claim 8, characterized in that the displayunit (11) is constructed to illustrate graphically the contours of theobject in the projection plane of the optical device (3) in response tocontrol instructions from the control and arithmetical unit (10).
 10. Anarrangement according to claim 5, characterized in that it furtherincludes a second elongated array of mutually adjacent radiationdetectors which is arranged on the level of the first mentioned array(9) and at right angles thereto and which is provided with an associatedoptical device for projecting an image of the object (1) on said secondarray in a direction perpendicular to the projection direction of thefirst mentioned optical device (3), and in that thecontrol-and-arithmetical unit (10) is also constructed to scan saidsecond array in the same manner as the first array (9).